What is the DS18B20 for?

Hi, 

Firstly, thanks to all the people that have replied to my other posts - its great to see such an active forum. I hope to return the favour when i'm up and running. 

I am .. 

a) still not convinced by the quality of my soldering.

b) still not convinced that the fundamentals of the HAH i've got a working. 

In particular, the reason for my concern is that i got to the part of the instructions where it said "Newer versions of the PCB make provision for an on-board DS18B20" and i noticed that i had soldered the jack for the RF unit in the wrong place. I managed to remove it but in the process don't think the PCB was in one piece. The soldering for the DS18B20 in the place its supposed to be isn't great for sure. 

What is this for? What will i notice not working if its not there?

At the moment i've

- configured twitter, posted a tweet and noticed that it deleted it ( as expected ) but didn't seem to send any xAP messages when i tweeted 'relay 1 on'

- been unable to get the LCD working, despite checking the soldering and cable. 

- seen that it'll find entries in my google calendar but doesn't seem to parse them correctly. 

- running 'lua clock.lua' from /etc/plugboard ( after copying it there ) doesn't seem to send any xAP events to the LCD ( checking via xfx viewer ). 

Any ideas?

Thanks ( again! )